Intra-aortic balloon catheter having an ultra-thin stretch blow molded balloon membrane

ABSTRACT

An intra-aortic balloon catheter having an ultra-thin stretch blow molded balloon membrane. The balloon membrane is made from thermoplastic elastomeric and/or semicrystalline materials such as but not limited to polyurethane and polyetheramid.

RELATED APPLICATIONS

[0001] This application is a continuation-in-part of, and claimspriority to, application Ser. No. 09/188,602, filed on Nov. 9, 1998.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The invention relates to an improved intra-aortic ballooncatheter. More particularly, the invention relates to an intra-aorticballoon catheter having an ultra-thin stretch blow molded balloonmembrane with improved abrasion resistance, fatigue life, andaneurization resistance.

[0004] 2. Description of the Prior Art

[0005] Intra-aortic balloon (IAB) catheters are used in patients withleft heart failure to augment the pumping action of the heart. Thecatheters, approximately 1 meter long, have an inflatable and deflatableballoon at the distal end. The catheter is typically inserted into thefemoral artery and moved up the descending thoracic aorta until thedistal tip of the balloon is positioned just below or distal to the leftsubclavian artery. The proximal end of the catheter remains outside ofthe patient's body. A passageway for inflating and deflating the balloonextends through the catheter and is connected at its proximal end to anexternal pump. The patient's central aortic pressure is used to time theballoon and the patient's ECG may used to trigger balloon inflation insynchronous counterpulsation to the patient's heart beat.

[0006] Intra-aortic balloon therapy increases coronary artery perfusion,decreases the workload of the left ventricle, and allows healing of theinjured myocardium. Ideally, the balloon should be inflating immediatelyafter the aortic valve closes and deflating just prior to the onset ofsystole. When properly coordinated, the inflation of the balloon raisesthe patient's diastolic pressure, increasing the oxygen supply to themyocardium; and balloon deflation just prior to the onset of systolelowers the patient's diastolic pressure, reducing myocardial oxygendemand.

[0007] Intra-aortic balloon catheters may also have a central passagewayor lumen which can be used to measure aortic pressure. In this duallumen construction, the central lumen may also be used to accommodate aguide wire to facilitate placement of the catheter and to infuse fluids,or to do blood sampling.

[0008] Typical dual lumen intra-aortic balloon catheters have an outer,flexible, plastic tube, which serves as the inflating and deflating gaspassageway, and a central tube therethrough formed of plastic tubing,stainless steel tubing, or wire coil embedded in plastic tubing. Apolyurethane compound is used to form the balloon.

[0009] All IAB catheters have two opposing design considerations. On theone hand, it is desirable to make the outer diameter of the entirecatheter as small as possible: to facilitate insertion of the catheterinto the aorta, maximizing blood flow past the inserted catheter, and toallow for the use of a smaller sheath to further maximize distal flow.On the other hand, however, it is desirable to make the inner diameterof the outer tube as large as possible because a large gas path area isrequired to accomplish the rapid inflation and deflation of the balloon.As a result of these opposing design considerations there is a need fora smaller catheter with a larger gas path area.

[0010] One method of making the outer diameter of the wrapped balloonportion of the catheter as small as possible is to wrap the balloon inits deflated state as tightly as possible around the inner tube.Wrapping the balloon tightly, however, has posed a number ofdifficulties. First, it is difficult to wrap the balloon tightly becauseof the friction between contacting surfaces of the balloon. Second,contacting surfaces of a tightly wrapped balloon may stick upon initialinflation. Datascope Investment Corp.'s co-pending application Ser. No.08/958,004, filed on Oct. 27, 1997, herein incorporated by reference inits entirety, discloses a lubricous coating for the balloon membranewhich solves the above mentioned problems. The coating allows theballoon membrane to be wrapped tightly more easily and prevents stickingof the balloon membrane upon initial inflation.

[0011] A second method of making the outer diameter of the wrappedballoon portion of the catheter as small as possible is to decrease thesize of the inner tube. Datascope Investment Corp.'s co-pendingapplication Ser. No. 08/958,004 also discloses an intra-aortic ballooncatheter with an inner tube having a smaller diameter only in theportion enveloped by the balloon membrane.

[0012] Although the above two methods have substantially reduced theoverall insertion size of the intra-aortic balloon catheter the needstill exists for greater size reduction. Furthermore, the need alsoexists for a balloon membrane with improved abrasion resistance, fatiguelife, and aneurization resistance. Currently, the method ofmanufacturing polyurethane balloon membranes is solvent casting. Thiscasting method does not provide the formed membrane with ideal physicaland mechanical properties. A solvent caste membrane with the basicmechanical properties necessary for balloon pumping, typically has asingle wall thickness of 4 to 6 mils (a mil is equal to one thousandthof an inch) which leads to a relatively large wrapped diameter of theballoon membrane. A thin solvent caste polyurethane membrane is capableof being manufactured, however, such a membrane does not demonstrate therequired abrasion resistance and fatigue life. Therefore, the needexists for an improved method of making a balloon membrane which willallow for a balloon membrane having a reduced thickness, and at thesame, having improved mechanical properties, including an improvedabrasion resistance, fatigue life, and aneurization resistance.

[0013] The present invention comprises an intra-aortic balloon catheterhaving a stretch blow molded balloon membrane. The balloon membrane ismade from thermoplastic elastomeric and/or semicrystalline materialssuch as but not limited to polyurethane and polyetheramid. As discussedabove, intra-aortic balloon membranes are generally solvent cast.

[0014] The process of stretch blow molding catheter balloon membranes isknown in the art. However, intra-aortic balloons have been traditionallymade by solvent casting because intra-aortic balloon membranes requirespecial characteristics: they must be substantially nondistensible andhave high abrasion resistance, fatigue life, and aneurizationresistance. Stretch blow molding has been traditionally used forangioplasty balloon membranes. These balloons are generally made fromPET, Nylon, or PEBAX materials. These materials achieve their highstrength at least partially because of the crystallization formed intheir microstructure during the initial stretching step of the tube andas a result of quickly cooling the tube to a temperature below thecrystallization temperature of the tube material. Crystallization of themicrostructure increases the strength of the balloon membrane, however,as the inventors of the present invention have discovered, it has anegative effect on the abrasion resistance and fatigue life of theballoon membrane. Given that angioplasty balloon/PTCA therapy is a shortduration therapy, crystallization is generally not a problem. Actually,it is quite useful given that it enhances the strength of the balloonmaterial. Intra-aortic balloon therapy, on the other hand, involvesrepetitive inflation and deflation of the balloon membrane over a longerperiod of time. Accordingly, it is known in the art that stretch blowmolded balloons are not appropriate for intra-aortic balloon membranes,which require high strength as well as high abrasion resistance andfatigue life.

[0015] The present invention overcomes the above described obstacle byrelying on the increased strength of polyurethane resulting from thehigh orientation and molecular interaction of the polyurethane moleculesalong the longitudinal axis of the tube. Said orientation results fromstretching the tube until substantially all stretchability is removed.Polyurethane, and the other materials listed in the present application,do not exhibit significant stress induced crystallization uponstretching. Accordingly, the inventors of the present invention havediscovered a means to create a balloon membrane strong enough to endureintra-aortic balloon pumping therapy without creating crystallizationmicrostructure, which they have discovered, is detrimental to theabrasion resistance and fatigue life of the balloon membrane.

[0016] U.S. Pat. No. 5,370,618 to Leonhardt discloses a pulmonary arteryballoon catheter comprising a catheter terminating in a blow moldedpolyurethane balloon membrane. Pulmonary artery catheters are generallyused for blood pressure measurements. Upon insertion and placement ofthe catheter the balloon membrane is inflated, occluding the housingblood vessel, so as to create a measurable pressure differential oneither side of the balloon membrane. In order to achieve completeocclusion of the housing blood vessel the pulmonary artery catheterballoon membrane is elastic so as to allow expansion of the membrane.This is in contrast to the balloon membrane of the present inventionwhich is stretch blow molded and is specifically manufactured tosubstantially eliminate distensibility in the final product.

SUMMARY OF THE INVENTION

[0017] Accordingly, it is an object of the invention to produce anultra-thin intra-aortic balloon membrane with superior abrasionresistance and fatigue life.

[0018] It is another object of the invention to produce a method formanufacturing said ultra-thin intra-aortic balloon membrane.

[0019] The invention is an intra-aortic balloon catheter having anultra-thin stretch blow molded balloon membrane. The balloon membrane ismade from thermoplastic elastomeric and/or semicrystalline materialssuch as but not limited to polyurethane and polyetheramid.

[0020] To the accomplishment of the above and related objects theinvention may be embodied in the form illustrated in the accompanyingdrawings. Attention is called to the fact, however, that the drawingsare illustrative only. Variations are contemplated as being part of theinvention, limited only by the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the drawings, like elements are depicted by like referencenumerals. The drawings are briefly described as follows.

[0022]FIG. 1 is longitudinal cross section of a prior art intra-aorticballoon catheter.

[0023]FIG. 1A is a transverse cross section of the prior artintra-aortic balloon catheter taken along line 1A-1A.

[0024]FIG. 2 is a longitudinal cross sectional view of a distal portionof the improved intra-aortic balloon catheter.

[0025]FIG. 3 is a side view of a mold having a balloon shaped cavityused to manufacture the balloon membrane.

[0026]FIG. 4 is a top view of the first half of the mold containing andsecuring a stretched tube used as a preform to create the balloonmembrane.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] The general structure of an intra-aortic balloon catheter is bestdescribed in relation to FIGS. 1 and 1A which illustrate a dual-lumenprior art intra-aortic balloon catheter. The catheter 1 is constructedof a plastic outer tube 2 forming a gas passageway lumen 3; and anotherplastic central tube 4 disposed within outer tube 2 and creating acentral passageway or lumen 5 as may best be seen in FIG. 1A.

[0028] A balloon 8 is disposed at the distal end of the catheter 1. Thedistal portion 7 of the central tube 4 extends beyond the distal end 10of outer tube 2. The distal end 8A of the balloon 8 is attached to a tip9 formed on the distal end 7 of central tube 4. The proximal end 8B ofthe balloon 8 is attached, by means of a lap joint, to the distal end 10of the outer tube 2. The distal portion 7 of the central tube 4 supportsthe balloon 8. Said distal portion 7 must have sufficient strength toprevent inversion of the balloon 8 as it inflates and deflates underaortic pressure, but at the same time, be flexible enough to be safelyinserted through an introducer sheath, moved through the arterial tree,and maintained in the thoracic aorta.

[0029] The balloon 8 is formed of a nonthrombogenic flexible material,such as polyurethane, and may have folds 11 formed as a result ofwrapping the balloon 8 about the central tube 4 to ease insertion of thecatheter 1. The balloon 8 has a single wall thickness of between 4 to 6mils. Radio-opaque bands 20 at the distal end of the catheter 1 aid inpositioning the balloon 8 in the descending aorta.

[0030] Inflation and deflation of the balloon 8 is accomplished throughthe gas passageway lumen 3. The central passageway or lumen 5 canaccommodate a guide wire for placement or repositioning of the catheter1. When the guide wire is not disposed in the central passageway orlumen 5, the central passageway or lumen 5 may be used for measuringblood pressure in the descending aorta. This pressure measurement may beused to coordinate the inflation and deflation of the balloon 8 with thepumping of the heart, however, use of the patient's ECG is preferred.Additionally, the central passageway or lumen 5 may be used to infuseliquids into the descending aorta, or to sample blood.

[0031] At the proximal end 12 of the catheter 1 a hub 13 is formed onthe proximal end 14 of the outer tube 2. The central passageway or lumen5 extends through the hub 13 and a connector 16 is provided at theproximal end 15 (or exit) of the central passageway or lumen 5.Measurement of aortic pressure and blood sampling may be done throughthe proximal end 15 of the central passageway or lumen 5.

[0032] The proximal end 18 of the gas passageway or lumen 3 exitsthrough a side arm 17 of the hub 13 on which is provided a connector 19.The proximal end 18 of the gas passageway or lumen 3 may be connected toan intra-aortic balloon pump.

[0033] The present invention comprises an intra-aortic balloon catheterhaving an ultra-thin stretch blow molded balloon membrane. FIG. 2illustrates a longitudinal cross sectional view of a distal portion ofan improved intra-aortic balloon catheter 30 of the present inventioncomprising an outer tube 32, an inner tube 33, a tip 34, and anultra-thin polyurethane balloon membrane 36. The tip 34 is connected toa distal end of the balloon membrane 36. A distal end of the outer tube32 is seamlessly welded to a proximal end of the balloon membrane 36.The balloon membrane 36 has a single wall thickness of between 1 to 2mils.

[0034] The balloon membrane 36 may be made from a variety ofthermoplastic elastomeric and/or semicrystalline materials including butnot limited to polyurethane and polyetheramid (known by its trade nameas PEBAX, produced by ELF-Atochem of Europe).

[0035] Another feature of the invention involves the attachment of theouter tube 32 and the balloon membrane 36. The distal end of the outertube 32 is seamlessly welded to the proximal end of the balloon membrane36. The distal end of the outer tube 32 has the same inner and outerdiameters as the proximal end of the balloon membrane 36, thus providinga smooth transition between the two parts without a constriction of thegas path. This is in contrast to the prior art catheter 1 of FIG. 2 inwhich the proximal end of the balloon 8 and the distal end of thecatheter 1 are attached by means of a lap joint. The lap joint isgenerally compressed during the manufacturing process in order to assurethat the outer diameter of the lap joint matches that of the outer tube2. Compression of the lap joint area leads to a restriction in the gasflow path. The present invention avoids this restriction through the useof a seamless weld.

[0036]FIG. 3 illustrates a side view of a mold 38 with tube clamps 44 onboth sides for securing a tube 46 having ends 50 to the mold 38. Themold 38 has a first half 40 and a second half 42 and is utilized in themanufacturing of the ultra-thin balloon membrane 36 to assure therequired profile of said balloon membrane 36. The first half of the mold40 and the second half of the mold 42 together define a balloon shapedcavity 48 illustrated in FIG. 3 as a shadowed segmented line.

[0037] The manufacturing process of the balloon membrane 36 comprisesthe following steps. First, a tube 46, as illustrated in FIG. 4, isstretched to the desired length of the balloon membrane 36. In thepreferred embodiment, and in this example, the tube 46 is 8 inches long,has a wall thickness of 0.02 inches, and is made from polyurethane;however, the tube 46 may be of a different size and may made from otherthermoplastic elastomeric and/or semicrystalline materials or othermaterials that do not display stress induced crystallization or acombination of such materials.

[0038]FIG. 4 illustrates a top plain view of the first half 40 of themold 38 which is identical to a view of the mold 38 taken along lines3A-3A. The ends 50 of the tube 46 are secured by means of the clamps 44(not shown in FIG. 4 for clarity) to opposite sides of the mold 38. Thesecond half 42 of the mold 38, as illustrated in FIG. 3, is attached tothe first half of the mold enclosing the stretched tube 46 in theballoon shaped cavity 48.

[0039] Stretching the tube 46, approximately two times its originallength, prior to blowing orientates the polyurethane molecules along thelongitudinal axis of the tube and substantially eliminates any furtherstretchability of the balloon membrane 36, at internal pressures of twoto four psi, by achieving a high molecular orientation and interaction.Note that this orientation and molecular interaction is achieved withoutsignificant crystallization; this is important to assure improvedabrasion resistance and fatigue life. Significant crystallization isdefined as any amount of crystallization which negatively affects theabrasion resistance and fatigue life of the balloon membrane.Polyurethane and polyetheramid, and other thermoplastic elastomericand/or semicrystalline materials, do not exhibit stress inducedcrystallization. This is in contrast to the materials traditionally usedfor stretch blow molded angioplasty balloon catheter membranes which onaverage have approximately 30% crystallization.

[0040] The stretching step assures the substantial nondistensibility ofthe final balloon membrane 36 under balloon innflation pressures ofapproximately 2-4 psi. This is in contrast to the pulmonary arteryballoon catheter, discussed above, whose polyurethane balloon membraneis specifically designed to be distensible so as to allow the membraneto expand, and thereby, occlude the blood vessel in which blood pressureis being measured.

[0041] The next manufacturing step involves filling the tube 46 with agas at approximately 150 psi, i.e. blowing the tube 46. The amount ofpressure applied depends on the grade of polyurethane: harder materialsrequire higher pressure. In all cases, however, the pressure must besufficient to force the tube 46 to take on the shape of the mold cavity48. The tube 46 is then heated above the tube melting temperature whilemaintaining a pressure of 30-40 psi in the tube 46. The final stepinvolves quickly cooling the ballooned tube 46, to a temperature abovethe crystallization temperature of the tube 46, while maintaining apressure of approximately 80 psi in the tube 46. The final thickness ofthe ballooned tube 46, approximately 0.002 inches, is significantlythinner than the prior art thickness of approximately 0.004-0.006inches.

[0042] It should be noted that the above detailed manufacturing processis merely an illustrative example and will vary for different sizedtubes and for tubes made of different materials. Manufacturing variablesinclude tube material, tube length, tube thickness, tube diameter, therequired pressure for blowing, the temperature for heating and coolingof the tube, and the amount of pressure maintained in the tube whileheating and cooling the tube.

[0043] It should further be noted that balloon membrane of the presentinvention may be used with any variation of intra-aortic ballooncatheters, including an intra-aortic balloon catheter having a co-lumencatheter, i.e. the inner lumen attached to or embedded in the catheterwall, or with any balloon catheter that requires a balloon membrane withimproved abrasion resistance and fatigue life.

What is claimed is:
 1. An intra-aortic balloon catheter comprising anouter tube with proximal and distal ends, and a stretch blow moldedballoon membrane with a proximal end connected to the distal end of theouter tube, said balloon membrane having been stretched without creatingsignificant crystallization to substantially eliminate stretchabilityunder balloon inflation pressures of approximately 2-4 psi.
 2. Theintra-aortic balloon catheter as claimed in claim 1 wherein the balloonmembrane is at least partially composed of a thermoplastic elastomericmaterial.
 3. The intra-aortic balloon catheter as claimed in claim 1wherein the balloon membrane is at least partially composed of asemicrystalline material.
 4. The intra-aortic balloon catheter asclaimed in claim 1 wherein the balloon membrane is at least partiallycomposed of a thermoplastic elastomeric semicrystalline material.
 5. Theintra-aortic balloon catheter as claimed in claim 1 wherein the balloonmembrane is at least partially composed of polyurethane.
 6. Theintra-aortic balloon catheter as claimed in claim 1 wherein the balloonmembrane is at least partially composed of polyetheramid.
 7. Theintra-aortic balloon catheter as claimed in claim 2 wherein the balloonmembrane is made from polyurethane.
 8. An intra-aortic balloon cathetercomprising an outer tube with proximal and distal ends, an inner tubehaving proximal and distal ends and extending beyond said distal end ofsaid outer tube, and a thermoplastic elastomeric balloon membrane with aproximal end attached to said distal end of said outer tube and a distalend connected to said distal end of said inner tube.
 9. The intra-aorticballoon catheter as claimed in claim 8 wherein the thermoplasticelastomeric balloon membrane is at least partially composed ofpolyurethane.
 10. The intra-aortic balloon catheter as claimed in claim8 wherein the thermoplastic elastomeric balloon membrane is at leastpartially composed of polyetheramid.
 11. The intra-aortic ballooncatheter as claimed in claim 8 wherein the proximal end of the balloonmembrane is seamlessly attached to the distal end of the outer tube andwherein the proximal end of the balloon membrane and the distal end ofthe outer tube have substantially the same thickness.
 12. Anintra-aortic balloon catheter comprising an outer tube with proximal anddistal ends, an inner tube having proximal and distal ends and extendingbeyond said distal end of said outer tube, and a semicrystalline balloonmembrane with a proximal end attached to said distal end of said outertube and a distal end connected to said distal end of said inner tube.13. The intra-aortic balloon catheter as claimed in claim 12 wherein thesemicrystalline balloon membrane is at least partially composed ofpolyurethane.
 14. The intra-aortic balloon catheter as claimed in claim12 wherein the semicrystalline balloon membrane is at least partiallycomposed of polyetheramid.
 15. The intra-aortic balloon catheter asclaimed in claim 12 wherein the proximal end of the balloon membrane isseamlessly attached to the distal end of the outer tube and wherein theproximal end of the balloon membrane and the distal end of the outertube have substantially the same thickness.
 16. A method for producingan ultra-thin balloon membrane for an intra-aortic balloon cathetercomprising the steps of: a) stretching a tube made from a thermoplasticelastomeric material without creating significant crystallization untilstretchability is substantially eliminated under balloon inflationpressures of approximately 2-4 psi; b) blowing the tube by increasingthe pressure within the tube until the tube has sufficiently ballooned;c) heating the ballooned tube; and d) cooling the ballooned tube toabove the crystallization temperature for the tube material.
 17. Themethod as claimed in claim 16 wherein a pressure above ambient ismaintained in the tube while heating and cooling to maintain theballooned shape of the tube.
 18. The method as claimed in claim 16wherein the tube is at least partially composed of a thermoplasticelastomeric material.
 19. The method as claimed in claim 16 wherein thetube is at least partially composed of a semicrystalline material. 20.The method as claimed in claim 17 wherein the tube is at least partiallycomposed of a thermoplastic elastomeric semicrystalline material. 21.The method as claimed in claim 17 wherein the tube is at least partiallycomposed of polyurethane.
 22. A method for producing an ultra-thinballoon membrane for an intra-aortic balloon catheter comprising thesteps of: a) stretching a tube made at least partially from asemicrystalline material; b) blowing the tube by increasing the pressurewithin the tube until the tube has sufficiently ballooned; c) heatingthe ballooned tube; and d) cooling the ballooned tube.
 23. The method asclaimed in claim 17 wherein the balloon membrane is at least partiallycomposed of polyetheramid.
 24. The method as claimed in claim 17 whereintube is placed in a mold having a cavity therein prior to blowing. 25.The method as claimed in claim 17 wherein a pressure above ambient ismaintained in the tube while heating and cooling to maintain theballooned shape of the tube.
 26. The method as claimed in claim 21wherein the tube is stretched to approximately 2 times its originallength.
 27. The intra-aortic balloon catheter as claimed in claim 1wherein the intra-aortic balloon catheter further comprises an innertube at least partially disposed within an outer surface of the outertube, a distal end of said inner tube being connected to a distal end ofthe balloon membrane.
 28. An intra-aortic balloon catheter comprising anouter tube with proximal and distal ends, and a stretch blow moldedpolyurethane balloon membrane with a proximal end connected to thedistal end of the outer tube, said balloon membrane having beenstretched without creating significant crystallization to substantiallyeliminate stretchability under balloon inflation pressures ofapproximately 2-4 psi.